I prefer wiggling my way out of crowds as soon as I can. For me
  it's strange: I can 'feel' people's emotions. i can rationally
  describe some of it if I have to.. but I can enter a room and
  feel anger in the air, happiness in the air... stuff like that.
  I mostly watch my emotions as they happen (years of anti-anxiety
  practice I guess) - but with other people,it just "hits me".
  Sucks me dry. == Me neither. I allow some people in but very
  few. Kids can usually come into the circle until they start
  playing the social awkwardness game like the adult world, then
  it's just more of the same. I like to keep ... hm - probably
  about the same radius as you if I can. Actually the boundaries
  of whatever room I'm in. I can tolerate closer to just past arms
  length, although I don't care for it, and anything close than
  arms like I just have this, "go go, move away" feeling inside
  that sometimes gets me to make an excuse and leave the room. ==
  When i had office work (I work from home now) - I'd walk at
  lunch time. Certain people I'd socialize lightly with: the
  people that got me coffee at Duncan Donuts were ok. I don't mind
  the scripted exchange at supermarkets and stuff. I know the
  various scripts and my part, so i -can- put an actor's face on
  for short periods of time. If I have to engage at length, I can
  do it if all I have to do is listen and go, "uh huh. yeah.
  right. OH How Interesting! - Yeah that must've been tough. Wow!
  Good for you!" at key moments. But I like to plan my routes when
  I can and be as efficient as possible generally. The people
  around me here are mostly chaotic and unpredictable. Sometimes I
  have to respond to their needs/wants and quickly, usually a
  dipomatic or psychoanalyst role. I can do those ok for short
  periods of time. But generally, Im behind my computer like now.
  ==